Most prior art codecs are a combination of analog input and digital output. A sigma-delta analog to digital converter (A/D) is scaled for a maximum output corresponding to the +3dbm0 code of the PCM data. The analog signal corresponding to this digital upscale value is far less than the maximum allowable dynamic range, which usually is limited by the supply range. This fact could potentially overload the A/D and consequently the digital filter. An FCC test, mandatory in the U.S., falls under this category. Once the digital filter overloads, internal clipping mechanisms prevent wrap around of the digital signal, thus creating a digital representation of a trapezoidal signal that contains harmonics with sufficient power to increase the FM modulation depth.